High speed electrical contact device including a rotating liquid contact element

ABSTRACT

An electrical contact device for high currents and high current pickup speeds comprises a ring-shaped rotating metallic contact element, with the inner circumference of which a roller-shaped contact element that is made of solid material and rotates about an axis, is in electrical contact. The speed on the circumference of the roller-shaped contact element fully or almost fully coincides with the speed on the inner circumference of the ringshaped contact element. The ring-shaped contact element consists of an highly electrically conductive contact liquid which is held in an open groove by centrifugal force. The contact resistance and the friction losses of the contact device are very small.

United States Patent 11 1 1111 3,835,436 Klaudy Sept. 10, 1974 1 HIGH SPEED ELECTRICAL CONTACT 3,444,408 5/1969 Krulls 310/178 DEVICE INCLUDING A ROTATING LIQUID 2,573,321] g/ garslon 210/219 CONTACT ELEMENT ,604, ru 5 10/178 Inventor: Peter Klaudy, Graz, Austria Siemens Aktiengesellschaft, Berlin & Munich, Germany Filed: May 22, 1973 App]. No.: 362,832

Assignee:

Foreign Application Priority Data May 23, 1972 Austria 4433/72 References Cited UNITED STATES PATENTS 6/1964 Ausfeld 200/166 BB 12/1966 Von Mossin 310/219 Primary Examiner-Robert K. Schaefer Assistant Examiner-William J Smith Attorney, Agent, or Firm-Kenyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT An electrical contact device for high currents and high current pickup speeds comprises a ring-shaped rotating metallic contact element, with the inner circumference of which a roller-shaped contact element that is made of solid material and rotates about an axis, is in electrical contact. The speed on the circumference of the roller-shaped contact element fully or almost fully coincides with the speed on the inner circumference of the ring-shaped contact element. The ring-shaped contact element consists of an highly electrically conductive contact liquid which is held in an open groove by centrifugal force. The contact resistance and the friction losses of the contact device are very small.

8 Claims, 4 Drawing Figures HIGH SPEED ELECTRICAL CONTACT DEVICE INCLUDING A ROTATING LIQUID CONTACT ELEMENT BACKGROUND OF THE lNVENTlON,

The invention relates to an electrical contact device for high currents and high current pickup speeds comprising a ring-shaped, rotating metallic contact element, with the inner circumference of which a rollershaped contact element that is made of solid material and which rotates about an axis, is in electrical contact, the speed on the circumference of the roller-shaped contact element fully or almost fully coinciding with the speed on the inner circumference of the ringshaped contact element.

The pickup of heavy current from fast moving machine parts, such as commutators, sliprings, rotor surfaces of homopolar machines etc, or from live rails for supplying track vehicles causes considerable difficulties when the amperage is high. Carbon brushes can be employed only for current densities of up to approx. to A/cm on the surface in contact with the moving element and only for slide speeds of up to about 50 m/s, since otherwise brief interruptions in the current arise due to mechanical and electrical reasons, which lead to arc phenomena and corrosion of the metallic surface of the sliprings or commutator segments on which the brushes slip. These difficulties cannot be avoided simply by increasing the contact pressure because heavier friction is thereby caused and thus unacceptable heating up and wear.

As known, it has already been suggested that current be effected by resorting to highly electrically con- .ductive contact liquids such as mercury, sodiumpotassiumetc. which are held in semiopened, rotating grooves by centrifugal force. A fixed contact element is immersed in the contact liquid around its entire circumference in these well-known contact devices.

In such contact devices, however, the friction between the fixed contact element sliding in the contact liquid and the contact liquid is proportional to the immersed surface of the fixed contact element in the contact liquid and it increases higher than to the second power with the slide speed. For technical reasons, the contact surface between the fixed contact element and the contact liquid cannot be kept at an arbitrarily low value with the object of limiting the friction losses, since the bearing play and thermal expansion which occur necessitate an immersion depth of at least 0.2 to 0.3 mm. Liquid contacts of this kind are therefore utilizable up to slide speeds of only approx. 40 to 50 m/s.

For the purpose of increasing this slide speed it has also been suggested (US. Pat. No. 3,604,967) that the rotary speed of the liquid metal over the surface of the contact ring be reduced by using intermediate rings. This measure leads to unstable behaviour, however.

It has furthermore been suggested (Austrian Patent 188,388 and British Patent 774,159) that the contact liquid be injected in a narrowly designed gap between a fixed contact element and a rotatingcontact element. The contact surface between the contact liquid and the rotating contact element, and thus the friction losses, can then be limited. The disadvantage of contacts of this type, however, lies in the fact that the speed of the contact liquid in the layer adjacent to the rotating contact element is greatly accelerated and the contact liquid after emerging from the contact gap is very finely atomized, accompanied by the formation of aerosol, on hitting the walls of the discharge duct, which leads to oxidation of the contact liquid and to sealing difficulties.

Roller contacts for transmitting high currents at high contact speeds have also been suggested. A contact device with roller contacts, described in German Patent 704,671, embodies a ring-shaped, rotating metallic contact element of solid material with the inner circumference of which a roller-shaped contact element of solid material revolvable around an axis is in electrical contact. Since the roller-shaped contact element is thereby driven by the ring-shaped contact element, the speed on the circumference of the rollershaped contact element roughly coincides with the speed on the inner circumference of the ring-shaped contact element of this contact device. In such contact devices with roller contacts, however, the occurrence of high current loads on the effective contact surfaces between the contact elements, the so-called Hertzian surface, causes local loosening of the metal material of the rollers due to heat developed by the current and the material flakes off under centrifugal force, which causes corrosion phenomena on the surface and thus an unacceptable increase in the contact resistance and arcing effects during prolonged operation.

SUMMARY OF THE INVENTION It is an object of the invention to avoid the described disadvantages in an electrical contact device used for high current and high current pickup speeds. In particular, the aim is to attain contact with minimum contact resistance and minimum friction losses. Furthermore, corrosion phenomena on the contact surfaces are to be avoided as far as possible.

To solve this problem, an electrical contact device according to the invention comprises a ring-shaped rotating metallic contact element with the inner circumference of which a roller-shaped contact element made of solid material and capable of rotating around an axis is in electrical contact, the speed on the'circumference of the roller-shaped contact element fully or almost fully coinciding with the speed on the inner circumference of the ring-shaped contact element, the ring shaped contact element consisting of highly electrically conductive contact liquid held, in an open groove by centrifugal force.

The peripheral speed of the roller-shaped contact element can be approximated to the speed on the inner circumference of the ring-shaped contact element, i.e. to the speed of the rotating contact liquid ring, by letting the roller-shaped contact element roll over the surface of the contact liquid.

It is even more advantageous if the roller-shaped contact element has a separate drive of its own which matches the speed on the circumference of the rollershaped contact element either fully or almost fully to the speed on the inner circumference of the ringshaped contact element.

It may also be advantageous if the surface of the roller-shaped contact element is provided with grooves.

BRIEF DESCRlPTlON OF THE DRAWINGS The invention is explained more closely by means of the drawings.

FIG. 1 shows an exemplary form of design of a contact device in accordance with the invention.

accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 exemplify an preferred form of design of a contact device in'accordance with the invention. FIG. 2 shows a cross-section through the device depicted in'FIG. 1, namely along the cross-section line II- II. The contact device comprises a ring-shaped contact element 1 made of an highly electrically conductive contact liquid, e.g. mercury, and a rollershaped contact element 2 made of solid contact material, e.g. an highly electrically conductive metal. The contact liquid ring I is held in a rotating groove 3 by centrifugal force, this groove being secured to a large contact disc 4 or to the rotor of a machine. Several roller-shaped contact elements 2 may also be provided. The roller-shaped contact elements 2 are well connected conductively with shafts 5, which are supported in bearings 6. The roller-shaped contact elements 2 are immersed somewhat along part of the roller surface in the rotating contact liquid ring 1. v

The peripheral speed v, of the contact roller 2 or contact rollers respectively is 50 selected that it equals or almost equals speed v of the rotating contact liquid ring 1. This can be attained, as already mentioned, by letting the contact roller 2 roll direct over the surface of the contact-liquid ring 1 or what is still more advantageous for avoiding undesirable slip by having contact roller 2 driven separately so that its surface speed coincides or almost coincides with the speed of the contact liquid. Slip friction between the contact liquid and the contact roller is then almost completely avoidable and the mechanical losses remain slight even 4 at high peripheral speeds of the contact liquid.

It can be seen from FIG. 1 that current I flows from the shaft 7 of the large contact disc 4 through the contact liquid ring 1, which rotates with the latter disc, and then to contact roller 2, which is in electrical contact with the contact liquid, after which it flows to shaft 5 of the contact roller 2, from which it can be picked up because of the lower peripheral speed of shaft 5 relative to that of disc 4 and liquid contact I via slip contacts 8 made of solid bodies, e.g. brushes, or by liquid contacts in the familiar way.

Experiments have shown that it is advantageous to provide the surface of the roller-shaped contact elements with grooves. FIGS. 3 and 4 depict such a contact roller 11 with grooves 12 on its circumference. It is advantageous to immerse the contact roller 11 in the contact liquid 13 only until the tooth-like protuberances between the grooves do not lie entirely in the contact liquid, i.e. so that the grooves 12 are not immersed in the contact liquid right down to their base. The contact liquid is then able to escape laterally into the vacated spacesnext to the teeth. Eddy formations and splashing are then avoided.

The idea on which the invention is based makes the latter on principle also suitable for current pickup by fast-moving vehicles from fixed live rails in which the contact liquid is located. 'The contact rollers would then be so driven that their peripheral speed would be zero or but a slight relative one compared to the moving contact liquid, despite the motion of the track vehicle.

What is claimed is:

1. An electrical contact device, comprising:

a first electrically conductive annular rotatable member including a radially inwardly directed groove;

an annular contact element, comprising an electrically conductive liquid, disposed in'said groove, said liquid being held in said groove by centrifugal force produced by rotation of said first rotatable member; and

a second electrically conductive annular rotatable member having the peripheral surface thereof in contact with said liquid contact element for electrically coupling said first rotatable member thereto, said second rotatable member being driven by said contact element so that the velocity of the radially inner surface of said contact element approximately equals the peripheral speed of said second rotatable member.

2. The electrical contact device recited in claim 1, wherein said second rotatable member is constructed of electrically conductive metallic material and has the peripheral surface thereof at least partially immersed in said electrically conductive liquid.

3. The electrical contact device recited in claim 1, wherein said second rotatable member further comprises a plurality of radially outwardly extending grooves disposed in the peripheral surface thereof.

4. The electrical contact device recited in claim 3, wherein said second rotatable member is positioned with respect to said firstrotatable member so that said peripheral grooves thereof are partially immersed in said electrically conductive liquid.

5. An electrical contact device, comprising:

a first electrically conductive annular rotatable member including a radially inwardly directed groove;

an annular contact element, comprising an electrically conductive liquid, disposed in said groove, said liquid being held in said groove by centrifugal force produced by rotation of said first rotatable member;

a second electrically conductive annular rotatable member having the peripheral surface thereof in contact with said liquid contact element for electrically coupling said first rotatable member thereto; and

means, coupled to said second rotatable member, for

driving said second member at a rotational speed at which the peripheral speed of said second rotatable member is approximately equal to the velocity of the radially inner surface of said contact element.

6. The electrical contact device recited in claim 5, wherein said second rotatable member is constructed of electrically conductive metallic material and has the peripheral surface thereof at least partially immersed in said electrically conductive liquid.

7. The electrical contact device recited in claim 5, wherein said second rotatable member further comprises a plurality of radially outwardly extending grooves disposed in the peripheral surface thereof.

8. The electrical contact device recited in claim 7, wherein said second rotatable member is positioned with respect to said first rotatable member so that said peripheral grooves thereof are partially immersed in said electrically conductive liquid. 

1. An electrical contact device, comprising: a first electrically conductive annular rotatable member including a radially inwardly directed groove; an annular contact element, comprising an electrically conductive liquid, disposed in said groove, said liquid being held in said groove by centrifuGal force produced by rotation of said first rotatable member; and a second electrically conductive annular rotatable member having the peripheral surface thereof in contact with said liquid contact element for electrically coupling said first rotatable member thereto, said second rotatable member being driven by said contact element so that the velocity of the radially inner surface of said contact element approximately equals the peripheral speed of said second rotatable member.
 2. The electrical contact device recited in claim 1, wherein said second rotatable member is constructed of electrically conductive metallic material and has the peripheral surface thereof at least partially immersed in said electrically conductive liquid.
 3. The electrical contact device recited in claim 1, wherein said second rotatable member further comprises a plurality of radially outwardly extending grooves disposed in the peripheral surface thereof.
 4. The electrical contact device recited in claim 3, wherein said second rotatable member is positioned with respect to said first rotatable member so that said peripheral grooves thereof are partially immersed in said electrically conductive liquid.
 5. An electrical contact device, comprising: a first electrically conductive annular rotatable member including a radially inwardly directed groove; an annular contact element, comprising an electrically conductive liquid, disposed in said groove, said liquid being held in said groove by centrifugal force produced by rotation of said first rotatable member; a second electrically conductive annular rotatable member having the peripheral surface thereof in contact with said liquid contact element for electrically coupling said first rotatable member thereto; and means, coupled to said second rotatable member, for driving said second member at a rotational speed at which the peripheral speed of said second rotatable member is approximately equal to the velocity of the radially inner surface of said contact element.
 6. The electrical contact device recited in claim 5, wherein said second rotatable member is constructed of electrically conductive metallic material and has the peripheral surface thereof at least partially immersed in said electrically conductive liquid.
 7. The electrical contact device recited in claim 5, wherein said second rotatable member further comprises a plurality of radially outwardly extending grooves disposed in the peripheral surface thereof.
 8. The electrical contact device recited in claim 7, wherein said second rotatable member is positioned with respect to said first rotatable member so that said peripheral grooves thereof are partially immersed in said electrically conductive liquid. 